Rectifier circuits that maintain a high efficiency over a wide dynamic range are essential in many AC-to-DC and RF-to-DC conversion applications, such as wireless power transfer (WPT) and wireless power harvesting (WPH) systems, power sensing and measurement, communication circuits and so on.
WPH and WPT systems performance can significantly benefit from wide dynamic range high efficiency rectifier circuits. WPH systems are designed to collect and harvest the ambient electromagnetic (EM) energy in the environment, convert it to DC and ultimately store the harvested energy and supply power to various devices and sensors. Typical applications of WPH systems include structural health monitoring systems (SHM), Internet of Things (IoT), large-terrain information gathering systems, etc. WPT systems are designed for contactless electrical power transfer between transmitters and receivers that are electrically or magnetically coupled together. Typical applications of WPT systems include RFID tags, biomedical implants, wireless charging of electronic devices and electrical vehicles, etc. In both WPH and WPT systems, the rectifier is one of the key components that converts the AC/RF power to DC. Because the AC/RF power provided to the rectifier device in both wireless power harvesting and wireless power transmission systems is subject to fluctuations, (for example due to variation of the ambient power density in WPH, and variation of distance between the transmitter and receiver in WPT systems) it is highly desirable for the rectifier used in a WPH and WPT systems to provide a wide dynamic range. This means that the rectifier should provide high efficiencies as input power level changes (i.e. to maintain high efficiencies over a large range of input power levels).
However, the dynamic range for conventional rectifier circuits is often very limited due to rectifying devices nonlinearities (diodes, transistors, etc.). The overall efficiency of the rectifiers (ηoverall) is determined by the ratio of the DC output power over the available power from the source, and is influenced by both the device rectification efficiency (ηrect) and the rectifier reflection coefficient (Γ), as described in equation (1):
                              η          overall                ⁢                  =          Δ                ⁢                                            P              dc                                      P              av                                =                                    (                              1                -                                                                          Γ                                                        2                                            )                        ⁢                          η              rect                                                          (        1        )            Γ is minimized when the RF or AC source is impedance matched to the rectifier circuit. If there is impedance mismatch between the source and the rectifier, a portion of the available power at the input to the rectifier is reflected thereby adversely impacting rectifier's efficiency. The rectifier's input impedance is power-dependent, making impedance matching very challenging as the input power level changes. Meanwhile, ηrect is also dependent on the input power level. For most rectifying devices, ηrect increases with the input power level until the device saturation point (Psat) where the breakdown effects become significant. Since both Γ and ηrect are dependent on the input power level, ηoverall is often optimized at a specific power level. Hence, ηoverall experience significant degradation as the input power to the rectifier varies away from its optimize level.
This disclosure describes novel wide dynamic range rectifier arrays capable of maintaining high rectification efficiencies as the input power varies. The wide dynamic range rectifier array consists of several rectifier circuits optimized for different power levels, as well as an adaptive power distribution network that delivers the AC or RF input power among these rectifier cells according to the power level. The rectifiers can use diodes or transistors and therefore the design approach described is very general. At lower power levels, most of the power is delivered to a rectifier optimized for low power operation; while at higher power levels, most of the power is delivered to the rectifier optimized for high power operation and so on. Following such an approach, high ηrect can be achieved over a wide range of power level variation. At the same time the dynamic impedance of different rectifier cells are transformed as a power level changes in such a way that they compensate each other's impedance variation as input power level changes. Consequently, the variation of the input impedance of the entire wide dynamic range rectifier array is made stable as power level varies. Therefore its input reflection coefficient of the rectifier array is maintained at low values as power level varies. Both improvement in ηrect and allow for high ηoverall to be achieved over a wide range of input power level variation.